In the medical industry, there is often a need for a laboratory technician, e.g., a cytotechnologist, to review a cytological specimen for the presence of specified cell types. For example, there is presently a need to review a cervico-vaginal Papanicolaou (Pap) smear slides for the presence of malignant or pre-malignant cells. Since its introduction over fifty years ago, Pap smears have been a powerful tool for detecting cancerous and precancerous cervical lesions. During that time, the Pap smear has been credited with reducing mortality from cervical cancer by as much as 70%. This once precipitous drop in the death rate has slowed however, and the mortality rate in the United States for this preventable disease has remained virtually constant, at about 5,000 per year since the mid-eighties. Therefore, about one-third of the 15,000 women diagnosed with cervical cancer annually still die, because the cancer was detected too late. A further cause for concern is National Cancer Institute data that shows an annual 3% increase in the incidence of invasive cervical cancer in white women under 50 years of age since 1986.
A number of factors may be contributing to this current threshold, not the least of which is the fact that many women, particularly in high risk populations, are still not participating in routine cervical cancer screening. Another contributing factor that has received much attention is the limitation of the traditional Pap smear method itself.
The reliability and efficacy of a cervical screening method is measured by its ability to diagnose precancerous lesions (sensitivity) while at the same time avoiding false positive diagnosis (specificity). In turn, these criteria are dependent on the accuracy of the cytological interpretation. The conventional Pap smear has false negative rates ranging from 10-50%. This is due in large part to the vast number of cells and objects (typically as many as 100,000 to 200,000) that must be reviewed by a technician to determine the possible existence of a small number of malignant or pre-malignant cells. Thus, Pap smear tests, as well as other tests requiring detailed review of biological material, have suffered from a high false negative rate due to fatigue imposed on the technician.
To facilitate this review process, automated biological screening (ABS) systems have been developed to focus the cytotechnologist's attention on the most pertinent cells, with a potential to discard the remaining cells from further review. A typical ABS system includes an imager, processor and automated viewing microscope. The imager acquires a series of images of a specimen slide, each image depicting a different portion of the slide. The processor then processes these images to identify the most pertinent biological objects for subsequent viewing by a technician, and their locations (x-y coordinates) in the frame. This information is then passed onto the microscope, which automatically proceeds to the x-y coordinates and centers on the biological objects for review by the technician. Alternatively, images of suspicious biological objects may be presented for viewing on a monitor.
The robotics used in ABS systems to handle and place large volumes of sample slides is bulky, complicated, and expensive. Also, the slide cassettes needed to store a large volume of sample slides are bulky and make archiving sample slides a costly endeavor. Accordingly, there remains a need for a more simple and less expensive device and method for handling and storing large volumes of biological samples.